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Purpose of Gear Diagnostics and Rack Mesh Characteristics

Aug 4, 2023 | Technical Literature | 0 comments

The application of gears in transmission appeared very early. More than 300 BC, the ancient Greek philosopher Aristotle explained the problem of using bronze or cast iron gears to transmit rotary motion in “Mechanical Problems”. A complete set of wheel trains has been applied to the guide car invented in ancient China. However, the ancient gears were made of wood or metal, which could only transmit the rotary motion between the shafts, and the stability of the transmission could not be guaranteed, and the load-carrying capacity of the gears was also very small.

The purpose of simple diagnosis is to quickly judge whether the gear is in normal working condition, and further conduct precise diagnostic analysis or take other measures for gear processing for gears in abnormal working condition. Of course, in many cases, some obvious faults can also be diagnosed based on a simple analysis of the vibration.
The simple diagnosis of gears includes noise diagnosis method, vibration diagnosis method and shock pulse (SPM) diagnosis method, etc., and vibration diagnosis method is the most commonly used. The vibration diagnosis method is a diagnostic method that uses the vibration intensity of the gear to judge whether the gear is in a normal working state. According to different judgment indicators and standards, it can be divided into absolute value judgment method and relative value judgment method.

Introduction to the structure of gears: Generally, there are gear teeth, tooth grooves, end faces, legal faces, addendum circles, dedendum circles, base circles, and indexing circles for gear processing.
Gear teeth: referred to as teeth, are the protruding parts on the gears used for meshing. These protruding parts are generally arranged in a radial pattern, and the teeth on the mating gears are in contact with each other, so that the gears can continue to mesh.
Tooth slot: the space between two adjacent teeth on the gear; the end face is the plane perpendicular to the axis of the gear or worm on the cylindrical gear or cylindrical worm. The normal plane: refers to the plane perpendicular to the tooth line of the gear teeth.
Addendum circle: refers to the circle where the top of the tooth is located. Root circle: refers to the circle where the bottom of the groove is located.

The characteristics and conditions of gear rack meshing are as follows
1. When the rack and pinion mesh, the meshing gear processing line is a fixed straight line.
2. When the gear meshes with the rack, the pitch circle of the gear always coincides with the pitch circle, no matter whether it is installed standardly or not.

The necessary conditions for gears and racks to mesh are: equal modules and equal tooth profile angles (pressure angles).
1. If the gear is a standard gear, the distance is the radius of the pitch circle of the gear. That is, the index line of the rack ((standard rack) is tangent to the index circle of the gear.
2. If it is a displacement gear, when designing the rack, you can always find out and calculate the pitch circle of the gear and the pitch line of the rack. The pitch circle of the gear is tangent to the pitch line of the rack, and the distance is the pitch circle radius.

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